1. Field of the Invention
This invention relates to a sealing device assembly disposed between two members rotatable relative to each other, particularly, two members one of which is rotatable and the other is fixed, such as the inner and outer races of an antifriction bearing, and more particularly to a sealing device assembly provided with at least three seal portions.
2. Description of the Prior Art
In mechanical apparatuses, there are known various types of sealing structure assemblies in which the space between a rotary shaft and a housing containing bearings associated with the rotary shaft or between members rotatable relative to each other such as the rings of individual antifriction bearings is reliably sealed by a method of continuously separating the apparatus into sealed chambers for the purpose of preventing leakage of lubricant from the apparatus or entry of dust or extraneous contaminants into the apparatus.
In an example of the prior art made from such a viewpoint (European patent application No. 0,051,170), as shown in FIG. 1 of the accompanying drawings, the sealing device assembly is designated by reference numeral 1 and is interposed between a rotary shaft 2 and a seat 3 formed on a housing 4 coaxially with the rotary shaft. The sealing device assembly 1 (FIG. 1) is comprised of a sealing ring 5 and a rigid shield member 6 fixed to the shaft 2. The sealing ring 5 has an annular support member 7 formed of a metal or other rigid material of high resistance, and a sealing member 8 made of a flexible and resiliently deformable material is secured to the support member 7.
The cross-section of the support member 7 is of an L-shape, and a first portion 9 thereof is parallel to the axis of the shaft and a second portion 10 thereof is perpendicular to the other portion and extends out radially relative to the axis of the shaft. On the other hand, the sealing member 8 includes a portion 11 which is parallel to the portion 10 of the member 7 and substantially flat. Two annular lips extend out from this portion 11. The first annular lip 12 extends out substantially in parallelism to the axis of the shaft 2 and moreover in a state inclined by a predetermined small angle in a direction away from the axis of the sealing member itself. On the other hand, the second annular lip 13 extends out from the base of the first lip 12 of the portion 11 in a predetermined slightly inclined state and in a direction substantially perpendicular to the axis of the sealing member itself. The end portions 14 and 15 of the two lips 12 and 13 are so formed as to be slidable on the surfaces 20 and 21, respectively, of the shield member 6. The shield member 6 is comprised of a sleeve portion 22 of a suitable thickness and a flange portion 23 perpendicular to the sleeve portion. The support member 7 can be fitted in the seat formed in the housing 4, against movement, and is coupled to the housing 4 by the portion 9 thereof.
The sealing device assembly 1 operates in the following manner.
The sealing ring 5 is fixed to the seat 3 formed on the housing 4 by the portion 9. Subsequently, the rigid shield member 6 is mounted by being pushed along the shaft 2 until the flange portion 23 becomes flush with the edge 16 of the portion 9. In this manner, the lips 12 and 13 are resiliently deformed and the end portions 14 and 15 thereof come into contact with the surface 20 of the flange portion 23 and the surface 21 of the sleeve portion 22, respectively.
The end portion 14 faces the environment, while the end portion 15 faces an interior chamber 17 defined by the seat 3 and the shaft 2. The lubricant which may leak from the annular chamber 17 meets the annular lip 13 which slides while being urged against the surface 21 of the sleeve portion 22 with a predetermined pressure. The end portion 15 of the lip 13 faces the interior of the interior chamber 17 and therefore, the stronger is the pushout force of the lubricant which tends to leak out, the greater is the sealing effect.
In contrast, extraneous contaminants which tend to enter the chamber 17 meet the annular lip 12 which slides while keeping contact with the surface 20 of the flange portion 23 with a predetermined pressure. The end portion 14 of the lip 12 faces the environment and therefore, in this case, the greater is the increase in the pressure with which the contaminants act on the sealing portion, the more is increased the pressure of contact between the surface 20 and the lip 12 and the more is increased the sealing effect.
The above-described prior art is effective in preventing the lubricant from leaking out from the interior of the mechanical apparatus and also preventing extraneous contaminants from entering the interior of the mechanical apparatus. However, if a contaminant such as muddy water from the outside adheres to the vicinity of the first annular lip 12, the contaminant will intervene between the lip 12 and the surface 20 to abrade the lip 12, thus expediting the entry of muddy water. Also, since the lips 12 and 13 face in said directions, the interior of the annular chamber surrounded by the lips 12, 13 and the shield member 6 assumes a negative pressure with respect to the ambience due to a temperature change and thus, the lips will be intensely urged against the sliding surface, thereby expediting abrasion of the lips.
Also, the provision of only two lips (lips 12 and 13) leads to an insufficient sealing effect in respect of both the prevention of leakage of the lubricant and the prevention of entry of contaminants.